/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec.marshalling;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ReplayingDecoder;
import io.netty.handler.codec.TooLongFrameException;
import org.jboss.marshalling.ByteInput;
import org.jboss.marshalling.Unmarshaller;

import java.io.ObjectStreamConstants;
import java.util.List;

/**
 * {@link ReplayingDecoder} which use an {@link Unmarshaller} to read the Object
 * out of the {@link ByteBuf}.
 *
 * If you can you should use {@link MarshallingDecoder}.
 */
public class CompatibleMarshallingDecoder extends ReplayingDecoder<Void>
{
    protected final UnmarshallerProvider provider;

    protected final int maxObjectSize;

    private boolean discardingTooLongFrame;

    /**
     * Create a new instance of {@link CompatibleMarshallingDecoder}.
     *
     * @param provider the {@link UnmarshallerProvider} which is used to obtain
     *        the {@link Unmarshaller} for the {@link Channel}
     * @param maxObjectSize the maximal size (in bytes) of the {@link Object} to
     *        unmarshal. Once the size is exceeded the {@link Channel} will get
     *        closed. Use a a maxObjectSize of {@link Integer#MAX_VALUE} to
     *        disable this. You should only do this if you are sure that the
     *        received Objects will never be big and the sending side are
     *        trusted, as this opens the possibility for a DOS-Attack due an
     *        {@link OutOfMemoryError}.
     */
    public CompatibleMarshallingDecoder(UnmarshallerProvider provider,
            int maxObjectSize)
    {
        this.provider = provider;
        this.maxObjectSize = maxObjectSize;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf buffer,
            List<Object> out) throws Exception
    {
        if (discardingTooLongFrame)
        {
            buffer.skipBytes(actualReadableBytes());
            checkpoint();
            return;
        }

        Unmarshaller unmarshaller = provider.getUnmarshaller(ctx);
        ByteInput input = new ChannelBufferByteInput(buffer);
        if (maxObjectSize != Integer.MAX_VALUE)
        {
            input = new LimitingByteInput(input, maxObjectSize);
        }
        try
        {
            unmarshaller.start(input);
            Object obj = unmarshaller.readObject();
            unmarshaller.finish();
            out.add(obj);
        }
        catch (LimitingByteInput.TooBigObjectException ignored)
        {
            discardingTooLongFrame = true;
            throw new TooLongFrameException();
        }
        finally
        {
            // Call close in a finally block as the ReplayingDecoder will throw
            // an Error if not enough bytes are
            // readable. This helps to be sure that we do not leak resource
            unmarshaller.close();
        }
    }

    @Override
    protected void decodeLast(ChannelHandlerContext ctx, ByteBuf buffer,
            List<Object> out) throws Exception
    {
        switch (buffer.readableBytes())
        {
            case 0:
                return;
            case 1:
                // Ignore the last TC_RESET
                if (buffer.getByte(
                        buffer.readerIndex()) == ObjectStreamConstants.TC_RESET)
                {
                    buffer.skipBytes(1);
                    return;
                }
        }

        decode(ctx, buffer, out);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception
    {
        if (cause instanceof TooLongFrameException)
        {
            ctx.close();
        }
        else
        {
            super.exceptionCaught(ctx, cause);
        }
    }
}
